UV background fluctuations traced by metal ions at $z\approx 3$

Here we investigate how LyC-opaque systems present in the intergalactic medium at $z\approx 3$ can distort the spectral shape of a uniform UV background (UVB) through radiative transfer (RT) effects. With this aim in mind, we perform a multi-frequency RT simulation through a cosmic volume of $10h^{-1}$~cMpc scale polluted by metals, and self-consistently derive the ions of all the species. The UVB spatial fluctuations are traced by the ratio of He\, \rm \scriptstyle II\ and H\, \rm \scriptstyle I\ column density, $\eta$, and the ratio of C$\mathrm{I}\mathrm{V}$ and Si$,{\rm {\scriptstyle IV\ }}$opticaldepths,$\zeta$\mathrm{.}Wefindthat:(i)$\eta$spatiallyfluctuatesthroughover-densesystems($\Delta$) with statistically significant deviations $\delta \eta >25$% in 18% of the volume ; (ii) same fluctuations in $\zeta$ are also present in $34$% of the enriched domain (only 8% of the total volume) and derive from a combination of RT induced effects and in-homogeneous metal enrichment, both effective in systems with $\Delta > 1.5$.